There's little better than working a classic joke into an appropriate context within a gaming session. For some people, anyway.

Make sure you have a good repertoire of them ready for any occasion.

Transcript

GM: This walker fires on the Ewocs.
[SFX]: Pow! Pow!
C-3PO: Fire the catapults!
[SFX]: boink! doink!
GM: The rocks hit, but bounce off harmlessly.
C-3PO: They're chickens!
GM: Armoured chickens. With laser beaks and laser ears.
[SFX]: Pow! Pow!
C-3PO: Chickens don't have ears.
R2-D2: Then how do they hear?
C-3PO: Terrible!
{beat}
[SFX]: Pow! Pow!